LOS ANGELES (Zap2it.com) When "Will & Grace" begins its eighth and final season Thursday (Sept. 29) with a live episode, the show's famously giggly cast will try to keep things running smoothly and avoid a "Carol Burnett Show"-esque meltdown.

She's kidding, of course (although maybe it's a good thing that the show will be on a seven-second delay). But like her castmates, Messing is both excited and a little apprehensive about doing a show without the luxury of a second take.

"When we first started and found out we were doing a live premiere, I was like, 'Yeah! That's fantastic, that's so exciting,'" Messing says during an interview session on Monday. "Now, officially about two hours ago, I realized I'm absolutely petrified."

The episode picks up shortly after the events of last May's finale, when Grace dallied with a married man (guest star Eric Stoltz) and Will spotted Karen's (Megan Mullally) presumed-dead ex, Stan. Stoltz and Alec Baldwin, who also appeared in the season finale, will reprise their roles.

The cast will do two live shows for NBC Thursday, one at 8:30 p.m. ET for viewers in the eastern half of the country and another at 8:30 PT for West Coast. In between, the writers will make some changes to jokes that don't go over that well with the live audience -- something that usually happens during breaks in filming of a normal episode.

"I think both shows will be good," Mullally says. "The script we're working with right now is very funny. But that's what the writers do anyway, they punch up [jokes] after the first pass. So it's kind of the same theory."

What's out of their control, though, is the audience. By showtime Thursday, the cast will have done as many as 10 run-throughs of the episode, including several in front of invited audiences, to nail down its timing. But if the audience is especially jovial, the cast may have to wait out some long laugh breaks.

"My biggest fear is, with all the jokes you have to hear the first four words. You have to hear the setup," McCormack says. "Sometimes [at tapings] our director makes us go back because the audience is still laughing at the previous thing and misses the setup. And that's the thing -- we'll have to really override the laughter."

Sean Hayes, whose Jack McFarland is embarking on a new career as a talk-show host, acknowledges that working live might invite a gaffe (so does NBC, for that matter; its promos for the episode feature Hayes getting bonked in the head by a boom mike). But he says he won't try to make his fellow actors slip up.

"I think it's probably corny to give them something that looks like a mistake," he says. "To force it is kind of like -- I won't reference the show, but to force, 'Oh, I'm breaking myself up,' I'm not a big fan of that."